github.com/ylsgit/go-ethereum@v1.6.5/whisper/whisperv5/topic.go (about)

     1  // Copyright 2016 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  // Contains the Whisper protocol Topic element.
    18  
    19  package whisperv5
    20  
    21  import (
    22  	"fmt"
    23  	"strings"
    24  
    25  	"github.com/ethereum/go-ethereum/common"
    26  )
    27  
    28  // Topic represents a cryptographically secure, probabilistic partial
    29  // classifications of a message, determined as the first (left) 4 bytes of the
    30  // SHA3 hash of some arbitrary data given by the original author of the message.
    31  type TopicType [TopicLength]byte
    32  
    33  func BytesToTopic(b []byte) (t TopicType) {
    34  	sz := TopicLength
    35  	if x := len(b); x < TopicLength {
    36  		sz = x
    37  	}
    38  	for i := 0; i < sz; i++ {
    39  		t[i] = b[i]
    40  	}
    41  	return t
    42  }
    43  
    44  // String converts a topic byte array to a string representation.
    45  func (topic *TopicType) String() string {
    46  	return string(common.ToHex(topic[:]))
    47  }
    48  
    49  // UnmarshalJSON parses a hex representation to a topic.
    50  func (t *TopicType) UnmarshalJSON(input []byte) error {
    51  	length := len(input)
    52  	if length >= 2 && input[0] == '"' && input[length-1] == '"' {
    53  		input = input[1 : length-1]
    54  	}
    55  	// strip "0x" for length check
    56  	if len(input) > 1 && strings.ToLower(string(input[:2])) == "0x" {
    57  		input = input[2:]
    58  	}
    59  	// validate the length of the input
    60  	if len(input) != TopicLength*2 {
    61  		return fmt.Errorf("unmarshalJSON failed: topic must be exactly %d bytes", TopicLength)
    62  	}
    63  	b := common.FromHex(string(input))
    64  	if b == nil {
    65  		return fmt.Errorf("unmarshalJSON failed: wrong topic format")
    66  	}
    67  	*t = BytesToTopic(b)
    68  	return nil
    69  }